Cast U&U

Separate U from U ... and put them back.
Two U-shaped bolts and four nuts - this looks like a combination of spare parts but looks are deceiving. This puzzle comes with a deviously hidden trick.
The key to unlocking these parts is to look carefully at each part first.
Theme: Complexity Level 4/6. Package size: 7,5 cm x 11,5 cm x 4,5 cm.
Designed by: Kyoo Wong. 2014 Puzzle Design Competition Jury Grand Prize.